Fragmentation Rates of Aromatic Radical Anions and the π*— σ* Orbital Crossing Point

Abstract
The reaction coordinate of the fragmentation of aromatic radical anions with nucleofugal groups was studied by the INDO and MNDO techniques. The reaction coordinate turned out as the stretching between the nucleofugal group bonded to the carbon atom of the aryl moiety. It was found that to fragment a π* radical anion, the odd electron has to be transferred to the σ* molecular orbital of the aryl-nucleofugal bond by an orbital crossing, which is reached by the lengthening of this bond. There is a qualitative agreement between the length of the bond to reach the orbital crossing point and the experimental fragmentation rates of the aromatic radical anions. Finally, some considerations about the σ-π coupling are made, since it is defining the possibility of a transfer from the π* to the σ* molecular orbital.

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